Abstract: In order to explore the relationship between the cold resistance of different alfalfa materials and the changes of antioxidant enzyme activity in alfalfa root crown under low temperature stress,sickle alfalfa (Medicago falcata L.) and four alfalfa (Medicago sativa L.) varieties were planted in Horqin sandy land. Overwintering organs were harvested before winter,and were treated with -10℃,-15℃,-20℃,-25℃ and -30℃. The antioxidant enzyme activity and relative conductivity of alfalfa root neck were measured with low temperature (4℃) storage as control (CK). Fitting logistic regression equation with relative conductivity to calculate semi-lethal temperature (LT₅₀) of alfalfa. The correlation between LT₅₀ and antioxidant enzyme activity was analyzed. The results showed that the cold resistance of sickle alfalfa was stronger than that of Medicago sativa. Among Medicago sativa,‘polar bear’ had the strongest cold resistance while ‘Knight T’ had the weakest. LT₅₀ was negatively correlated with antioxidant enzyme activities at different temperatures. The uperoxide dismutase (SOD) and Catalase (CAT) activities in alfalfa root crown under -30℃ treatment had significant and extremely significant negative correlation with LT₅₀. Conclusion:alfalfa enhanced cold resistance by increasing SOD and CAT activities. SOD activity at -30℃ and CAT activities at -10℃ and -30℃ can be used as physiological indexes of alfalfa cold resistance.

Key words: Low temperature stress, Alfalfa, Antioxidant enzymes, Cold resistance

摘要： 为探究不同苜蓿材料的抗寒性与低温胁迫下苜蓿根颈抗氧化酶活性变化的关系，本研究在科尔沁沙地种植黄花苜蓿（Medicago falcata L.）和4个紫花苜蓿（Medicago sativa L.）品种，越冬前挖取越冬器官并进行-10℃，-15℃，-20℃，-25℃，-30℃低温胁迫处理，以低温（4℃）贮藏为对照，测定苜蓿根颈抗氧化酶活性及相对电导率，利用相对电导率值拟合Logistic回归方程计算苜蓿半数致死温度（LT₅₀），进行LT₅₀与抗氧化酶活性相关性分析。结果表明，黄花苜蓿的抗寒性强于紫花苜蓿，其中紫花苜蓿‘北极熊’品种抗寒性最强，‘骑士T’品种最弱。LT₅₀与不同温度处理下抗氧化酶活性呈负相关，在-30℃处理下超氧化物歧化酶（Superoxide dismutase，SOD）活性和过氧化氢酶（Catalase，CAT）活性分别与LT₅₀呈显著和极显著负相关。综上所述，苜蓿通过提高SOD，CAT活性增强抗寒性，-30℃处理下的SOD活性和-10℃，-30℃处理下CAT活性可以作为衡量苜蓿抗寒性强弱的生理指标。

关键词: 低温胁迫, 苜蓿, 抗氧化酶, 抗寒性